U.S. patent number 7,894,505 [Application Number 11/785,743] was granted by the patent office on 2011-02-22 for apparatus and method for selecting effective channel in a multi-user mimo system.
This patent grant is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Ho-Jin Kim, Sung-Jin Kim, JianJun Li, Yong-Xing Zhou.
United States Patent |
7,894,505 |
Zhou , et al. |
February 22, 2011 |
Apparatus and method for selecting effective channel in a
multi-user MIMO system
Abstract
An apparatus and method for selecting an effective channel in a
multi-user MIMO system are provided, in which a receiver receives
pilot signals from a transmitter, determines channel information
indicating an antenna offering the best quality among a plurality
of antennas using the pilot signals, and generates feedback
information with the channel information, and the transmitter
receives feedback information from a plurality of receivers,
generates a channel matrix using the feedback information, and
transmits data simultaneously to the plurality of receivers using
the channel matrix.
Inventors: |
Zhou; Yong-Xing (Yongin-si,
KR), Kim; Sung-Jin (Suwon-si, KR), Li;
JianJun (Yongin-si, KR), Kim; Ho-Jin (Seoul,
KR) |
Assignee: |
Samsung Electronics Co., Ltd.
(Suwon-si, KR)
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Family
ID: |
38817988 |
Appl.
No.: |
11/785,743 |
Filed: |
April 19, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070253508 A1 |
Nov 1, 2007 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60792975 |
Apr 19, 2006 |
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Current U.S.
Class: |
375/141; 370/318;
375/358; 455/24; 455/226.1; 375/267; 375/341; 375/146; 370/282;
370/465; 455/13.4; 455/67.13 |
Current CPC
Class: |
H04B
7/0626 (20130101); H04L 1/0026 (20130101) |
Current International
Class: |
H04B
1/00 (20060101) |
Field of
Search: |
;375/141,146,147,267,299,341,358,219-222
;370/275,282,318-321,329-330,335,336,340,342,345,436,437,441,442,465,478-480,491,498
;455/13.4,24,500,67.11,67.13,69,561,562.1,101,115.1,127.1,226.1-226.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10-2002-0008301 |
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Jan 2002 |
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KR |
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10-2005-0055592 |
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Jun 2005 |
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KR |
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10-2006-0054155 |
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May 2006 |
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KR |
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10-2006-0068082 |
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Jun 2006 |
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KR |
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Primary Examiner: Ha; Dac V
Attorney, Agent or Firm: NSIP Law
Parent Case Text
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This application claims the benefit under 35 U.S.C. .sctn.119(e) of
U.S. Provisional Patent Application No. 60/792,975, filed on Apr.
19, 2006, in the U.S. Patent and Trademark Office, the entire
disclosure of which is hereby incorporated by reference.
Claims
What is claimed is:
1. A multi-user Multiple-Input Multiple-Output (MIMO) system,
comprising: a receiver configured to: receive pilot signals through
each of antennas from a transmitter; select an antenna having a
best channel quality among the antennas using the pilot signals;
and generate feedback information comprising channel information on
the selected antenna; and the transmitter configured to: receive
the feedback information from each of a plurality of receivers;
generate a channel matrix using the feedback information; and
transmit data simultaneously to the plurality of receivers using
the channel matrix, wherein the feedback information comprises a
Hermitian matrix comprising channel information .times.
##EQU00005## and channel noise UU.sub.k.sup.H, and wherein each of
V and U is a matrix obtained by SVD of a channel matrix H, .sup.H
is a Hermitian operator, and k is an integer.
2. A multi-user Multiple-Input Multiple-Output (MIMO) system,
comprising: a receiver configured to: receive pilot signals through
each of antennas from a transmitter; select an antenna having a
best channel quality among the antennas using the pilot signals;
and generate feedback information comprising channel information on
the selected antenna; and the transmitter configured to: receive
the feedback information from each of a plurality of receivers;
generate a channel matrix using the feedback information; and
transmit data simultaneously to the plurality of receivers using
the channel matrix, wherein the transmitter is further configured
to calculate backward filter information B.sub.block.sup.H, forward
filter information F.sub.block.sup.H, and a scaling factor
.beta..sub.block.sup.H for each of the receivers using the channel
information received from each receiver, and wherein .sup.H is a
Hermitian operator.
3. The multi-user MIMO system of claim 2, wherein the transmitter
is further configured to send the scaling factor to each
receiver.
4. The multi-user MIMO system of claim 2, wherein: the backward
filter information B.sub.block.sup.H comprises a unit lower
triangular matrix; and the transmitter is further configured to
control the power of transmission data using the backward filter
information B.sub.block.sup.H.
5. The multi-user MIMO system of claim 2, wherein: the transmitter
is further configured to calculate the forward filter information
F.sub.block.sup.H by
F.sub.block.sup.H=.beta..sub.block.sup.HH.sub.eff.sup.HP.sub.block.sup.TL-
.sub.block.sup.-HD.sub.block.sup.-1 in which D.sub.block is a
diagonal matrix; and the transmitter is further configured to
calculate the scaling factor .beta..sub.block.sup.H for each
receiver to satisfy a transmit power, wherein H is a channel
matrix.
6. The multi-user MIMO system of claim 2, wherein the scaling
factor .beta..sub.block.sup.H represents a modulo level of a modulo
operation performed in the transmitter.
7. A channel selection method in a multi-user Multiple-Input
Multiple-Output (MIMO) system, the method comprising: receiving
pilot signals through a plurality of antennas from a transmitter;
selecting an antenna having a best channel quality among the
antennas using the pilot signals by each of a plurality of
receivers; sending feedback information comprising channel
information on the selected antenna to the transmitter by each
receiver; receiving the feedback information from each of the
plurality of receivers; generating a channel matrix using the
feedback information by the transmitter; and transmitting data
simultaneously to the plurality of receivers using the channel
matrix, wherein the channel matrix generation comprises generating
the channel matrix comprising backward filter information
B.sub.block.sup.H, forward filter information F.sub.block.sup.H,
and a scaling factor .beta..sub.block.sup.H, the backward filter
information B.sub.block.sup.H, the forward filter information
F.sub.block.sup.H, and the scaling factor .beta..sub.block.sup.H
being calculated for the each receiver using the feedback
information received from the each receiver, and wherein .sup.H is
a Hermitian operator.
8. The channel selection method of claim 7, further comprising
sending the scaling factor to each receiver.
9. An apparatus of a receiver for extracting channel information in
a multi-user Multiple-Input Multiple-Output (MIMO) system, the
apparatus comprising: a receive beamformer configured to, upon
receipt of different signals through a plurality of antennas:
determine channel information indicating channel information using
the received signals; and send the channel information to a
transmitter; and a multiplier configured to, upon receipt of a
scaling factor from the transmitter, multiply an input signal by
the inverse of the scaling factor.
10. The apparatus of claim 9, wherein the scaling factor represents
a modulo level of a modulo operation performed in the
transmitter.
11. The apparatus of claim 9, wherein the channel information
extracted from the signals is calculated by obtaining decomposed
channel information by SVD (Singular Value Decomposition) and
multiplying the decomposed channel information by a channel
matrix.
12. The apparatus of claim 9, wherein the signals comprise pilot
signals.
13. An apparatus of a transmitter for selecting a channel in a
multi-user Multiple-Input Multiple-Output (MIMO) system, the
apparatus comprising: an extractor configured to, upon receipt of
channel information from a plurality of receivers, extract filter
information from the channel information; a Tomlinson-Harashima
Precoding (THP) part configured to control the power of data using
the filter information; and a beamforming part configured to
control beamforming for a plurality of antennas using the filter
information in order to simultaneously transmit the
power-controlled data to the plurality of receivers.
14. The apparatus of claim 13, wherein the THP part comprises: a
permutation matrix portion configured to order an input signal; a
backward filter configured to filter the ordered signal; and a
modulo operator configured to control the power of the signal
increased by the backward filter.
15. The apparatus of claim 13, wherein the channel information is
calculated by obtaining decomposed channel information by SVD
(Singular Value Decomposition) and multiplying the decomposed
channel information by a channel matrix.
16. The apparatus of claim 13, wherein the filter information
comprises backward filter information B.sub.block.sup.H, forward
filter information F.sub.block.sup.H, and a scaling factor
.beta..sub.block.sup.H, wherein .sup.H is a Hermitian operator.
17. The apparatus of claim 16, wherein: the backward filter
information B.sub.block.sup.H is unit lower triangular; and the THP
part is configured to control the power of the data using the
backward filter information B.sub.block.sup.H.
18. The apparatus of claim 16, wherein the extractor is further
configured to: calculate the forward filter information
F.sub.block.sup.H by
F.sub.block.sup.H=.beta..sub.block.sup.HH.sub.eff.sup.HP.sub.block.sup-
.TL.sub.block.sup.-HD.sub.block.sup.-1 in which D.sub.block is a
diagonal matrix; and calculate the scaling factor
.beta..sub.block.sup.H to satisfy a transmit power, wherein H is a
channel matrix.
19. The apparatus of claim 16, wherein the scaling factor
.beta..sub.block.sup.H represents a modulo level of a modulo
operation performed in the transmitter.
20. A method of a transmitter for selecting a channel in a
multi-user Multiple-Input Multiple-Output (MIMO) system, the method
comprising: extracting, upon receipt of channel information from a
plurality of receivers, filter information from the channel
information; controlling the power of data using the filter
information; and controlling beamforming for a plurality of
antennas using the filter information in order to simultaneously
transmit the power-controlled data to the plurality of
receivers.
21. The method of claim 20, wherein the channel information
represents the channel state of an antenna among antennas of each
of the receivers, comprising a Hermitian matrix H.sub.eff
comprising channel information and a channel noise, wherein H is a
channel matrix.
22. The method of claim 20, wherein the filter information
comprises backward filter information B.sub.block.sup.H, forward
filter information F.sub.block.sup.H, and a scaling factor
.beta..sub.block.sup.H, wherein .sup.H is a Hermitian operator.
23. The method of claim 22, wherein: the backward filter
information B.sub.block.sup.H is unit lower triangular; and the
power control comprises controlling the power of the data using the
backward filter information B.sub.block.sup.H.
24. The method of claim 22, wherein the extraction comprises:
calculating the forward filter information F.sub.block.sup.H by
F.sub.block.sup.H=.beta..sub.block.sup.HH.sub.eff.sup.HP.sub.block.sup.TL-
.sub.block.sup.-HD.sub.block.sup.-1 in which D.sub.block is a
diagonal matrix; and calculating the scaling factor
.beta..sub.block.sup.H to satisfy a transmit power.
25. The method of claim 22, wherein the beamforming control
comprises controlling the beamforming for the plurality of antennas
using the forward filter information F.sub.block.sup.H.
26. A computer-readable recording medium storing a program for
selecting a channel in a multi-user Multiple-Input Multiple-Output
(MIMO) system, comprising: a first set of instructions for
receiving pilot signals through a plurality of antennas from a
transmitter and selecting an antenna having a best channel quality
among the antennas using the pilot signals by each of a plurality
of receivers; a second set of instructions for sending feedback
information comprising channel information on the selected antenna
to the transmitter by each receiver; a third set of instructions
for receiving the feedback information from each of the plurality
of receivers and generating a channel matrix using the feedback
information by the transmitter; and a fourth set of instructions
for transmitting data simultaneously to the plurality of receivers
using the channel matrix, wherein the channel matrix generation
comprises generating the channel matrix comprising backward filter
information B.sub.block.sup.H, forward filter information
F.sub.block.sup.H, and a scaling factor .beta..sub.block.sup.H, the
backward filter information B.sub.block.sup.H, the forward filter
information F.sub.block.sup.H, and the scaling factor
.beta..sub.block.sup.H being calculated for the each receiver using
the feedback information received from the each receiver, and where
H is a matrix value.
27. A computer-readable recording medium storing a program for
selecting a channel in a multi-user Multiple-Input Multiple-Output
(MIMO) system, comprising: a first set of instructions for
extracting, upon receipt of channel information from a plurality of
receivers, filter information from the channel information; a
second set of instructions for controlling the power of data using
the filter information; and a third set of instructions for
controlling beamforming for a plurality of antennas using the
filter information in order to simultaneously transmit the
power-controlled data to the plurality of receivers.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to multi-user Multiple
Input Multiple Output (MIMO) system. More particularly, the present
invention relates to an apparatus and method for effectively
selecting the best channels for a plurality of receivers based on
effective channel information received from the receivers and
sending data simultaneously on the best channels to the receivers
in a multi-user MIMO system.
2. Description of the Related Art
In a system beyond the 3rd Generation (3G) system, for example, the
4th Generation (4G) system, both a wireless network and a Core
Network (CN) are characterized by ubiquitous and seamless
connection, high data rate, openness, and network convergence. The
4G system is designed to be capable of transmitting a large amount
of data, aiming at high data rate.
The 4G system will be configured in an integrated form rather than
in the form of a single network. That is, satellite networks,
Wireless Local Area Network (WLAN), Digital Audio Broadcast (DAB),
Digital Video Broadcast (DVB), and other networks will all be
merged into the 4G system. Owing to the network integration, data
or signals can be sent and received between a transmitter (for
example, Base Station (BS)) and a plurality of receivers (for
example, Mobile Stations (MSs)) by MIMO. To realize the MIMO
technology, the transmitter can be equipped with N transmit
antennas and the receivers can also have N receive antennas. As a
consequence, data rate can be increased.
Concurrent provisioning of a service to multiple users causes
multi-user interference, which can be cancelled by Dirty Paper
Coding (DPC). Among DPC techniques, a low-complexity,
high-performance Tomlinson-Harashima Precoding (THP) may be
used.
A shortcoming of THP is huge feedback information. Since a
plurality of receivers send feedback information about individual
transmit antennas to a transmitter, the load on the transmitter is
increased and overall system performance may be degraded.
Accordingly, there is a need for an apparatus and method for
selecting channel in a multi-user MIMO system that can reduce
feedback information between receivers and transmitters to reduce
the load on the transmitter and avoid degrading overall system
performance.
SUMMARY OF THE INVENTION
An aspect of the present invention is to address at least these
problems and/or disadvantages and to provide at least the
advantages described below. Accordingly, an aspect of the present
invention is to provide a multi-user MIMO system for reducing total
feedback information by allowing each receiver to send minimal
effective channel information to a transmitter.
Another aspect of the present invention provides an apparatus and
method of a receiver for detecting channel information using pilot
signals received from a transmitter and sending effective channel
information regarding the best channel state to the transmitter in
a multi-user MIMO system.
A further aspect of the present invention provides an apparatus and
method of a transmitter for selecting channel information for a
plurality of receivers based on channel information received from
the receivers in a multi-user MIMO system.
A further aspect of exemplary embodiments of the present invention
provides an apparatus and method for a computer-readable recording
medium for transmitting data simultaneously to a plurality of
receivers by using feedback information received from the plurality
of receivers, when the receiver detects channel information using
the received pilot signal, generates feedback information with the
detected channel information and then transmits the feedback
information to the transmitter.
A further aspect of exemplary embodiments of the present invention
provides an apparatus and method for a computer-readable recording
medium for determining channel information and storing a channel
information extracting program for transmitting the determined
channel information to the transmitter, when the transmitter
receives unique signal through the plurality of antennas.
A further aspect of exemplary embodiments of the present invention
provides an apparatus and method for a computer-readable recording
medium for storing a channel selection program for extracting, upon
receipt of channel information from a plurality of receivers,
filter information, controlling the power of data using the filter
information, and controlling beamforming for a plurality of
antennas using the filter information in order to simultaneously
transmit the power-controlled data.
In accordance with an aspect of the present invention, there is
provided a multi-user MIMO system, in which a receiver receives
pilot signals from a transmitter, determines channel information
indicating an antenna among a plurality of antennas using the pilot
signals, and generates feedback information with the channel
information, and the transmitter receives feedback information from
a plurality of receivers, generates a channel matrix using the
feedback information, and transmits data simultaneously to the
plurality of receivers using the channel matrix.
In accordance with another aspect of the present invention, there
is provided a channel selection method in a multi-user MIMO system,
in which each of a plurality of receivers receives pilot signals
through a plurality of antennas from a transmitter, measures the
best quality with respect to the plurality of antennas using the
pilot signals, and sends feedback information with channel
information indicating the channel information measurement to the
transmitter, and the transmitter receives the feedback information
from the plurality of receivers, generates a channel matrix using
the feedback information by the transmitter, and transmits data
simultaneously to the plurality of receivers using the channel
matrix.
In accordance with a further aspect of the present invention, there
is provided a method of a receiver for extracting channel
information in a multi-user MIMO system, in which the receiver
receives different signals through a plurality of antennas,
determines channel information indicating the best quality using
the received signals, and sends the channel information to a
transmitter.
In accordance with still another aspect of the present invention,
there is provided a method of a transmitter for selecting a channel
in a multi-user MIMO system, in which upon receipt of channel
information from a plurality of receivers, the transmitter extracts
filter information from the channel information, controls the power
of data using the filter information, and controls beamforming for
a plurality of antennas using the filter information in order to
simultaneously transmit the power-controlled data to the plurality
of receivers.
Other aspect, advantages and salient features of the invention will
become apparent to those skilled in the art from the following
detailed description, which, taken in conjunction with annexed
drawings, discloses the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and advantages of the present
invention will be more apparent from the following detailed
description taken in conjunction with the accompanying drawings, in
which:
FIG. 1 illustrates the configuration of a multi-user MIMO system
according to an exemplary embodiment of the present invention;
FIG. 2 is a flowchart illustrating a method for selecting the best
channel for a receiver in the multi-user MIMO system according to
an exemplary embodiment of the present invention;
FIG. 3 is a block diagram of a channel information extractor of a
receiver in the multi-user MIMO system according to an exemplary
embodiment of the present invention;
FIG. 4 is a flowchart illustrating a channel information extracting
method of the receiver in the multi-user MIMO system according to
an exemplary embodiment of the present invention;
FIG. 5 is a block diagram of a channel selector of a transmitter in
the multi-user MIMO system according to an exemplary embodiment of
the present invention; and
FIG. 6 is a flowchart illustrating a channel selection method of
the transmitter in the multi-user MIMO system according to an
exemplary embodiment of the present invention.
Throughout the drawings, the same drawing reference numerals will
be understood to refer to the same elements, features and
structures.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The matters exemplified in the following description are provided
to assist in a comprehensive understanding of the invention. Those
of ordinary skill in the art will recognize that various changes
and modifications of the embodiments described herein can be made
without departing from the scope and spirit of the invention. Also,
descriptions of well-known functions and constructions are omitted
for clarity and conciseness.
Exemplary embodiments of the present invention are intended to
provide a multi-user MIMO system. They are also intended to provide
an apparatus and method for selecting an effective channel in a
multi-user MIMO system.
FIG. 1 illustrates the configuration of a multi-user MIMO system
according to an exemplary embodiment of the present invention.
Referring to FIG. 1, the multi-user MIMO system can include a
transmitter (for example, a BS) 100 and a plurality of receivers
(for example, MSs) 200, 300 and 400.
According to an exemplary embodiment, the transmitter 100 precodes
a plurality of input user data u.sub.1, u.sub.2, . . . , u.sub.Nr
through a precoder and broadcasts the precoded data x.sub.1,
x.sub.2, . . . , x.sub.Nt to the receivers 200, 300 and 400 through
a plurality of transmit antennas. A receiver MS.sub.k receives the
broadcast data through a plurality of receive antennas. The total
number of receive antennas that the receivers have in the system is
calculated by
.times..ltoreq. ##EQU00001##
where Nr denotes the total number of receive antennas that the
receivers have in the system, Nr.sub.k denotes the number of
receive antennas in the receiver MS.sub.k, and Nt denotes the
number of the transmit antennas in the transmitter.
The transmitter sends the precoded signal x.sub.i (i=1, . . . , Nt)
to the receivers through the Nt transmit antennas. The received
signal at the receiver MS.sub.k is expressed as
y.sub.k=H.sub.kx+n.sub.k (2)
where x is [x.sub.1, x.sub.2, . . . , x.sub.Nt].sup.T([].sup.T
represents transposition), H.sub.k denotes an
Nr.sub.k.times.N.sub.t channel matrix, and n.sub.k denotes additive
Gaussian random noise for the receiver MS.sub.k.
According to equation (2), the received signal of all the receivers
is given by y=Hx+n (3)
where H=[H.sub.1.sup.T,H.sub.2.sup.T, . . . , H.sub.K.sup.T].sup.T,
y=[y.sub.1.sup.T,y.sub.2.sup.T, . . . , y.sub.K.sup.T].sup.T, and
n=[n.sub.1.sup.T,n.sub.2.sup.T, . . . , n.sub.K.sup.T].sup.T.
In the transmitter 100, the precoder reorders the input signal
vector u by a permutation matrix P. The permutation matrix P
specifies the ordering of THP, given as
yy.sub.k=UU.sub.k.sup.H(H.sub.kx+n.sub.k)=.SIGMA.VV.sub.k.sup.Hx+UU.sub.k-
.sup.Hn.sub.k (4)
The channel states between the transmit antennas of the transmitter
and the receive antennas of each receiver can be represented as a
Hermitian matrix and multi-user MIMO can be realized using these
antennas.
Also, in Equation 4,
.times. ##EQU00002## and UU.sub.k.sup.H are channel information
measured through pilot signal transmitted by the transmitter. The
receiver extracts channel information of a channel through the
pilot signal, decomposes the extracted channel matrix using a
method such as a Singular Value Decomposition(SVD), and extracts V
and U from the decomposed matrix. The receiver
singular-value-decomposes the extracted V and U.
In the multi-user MIMO system, the transmitter broadcasts pilot
signals periodically to the receivers.
All the receivers measures the qualities (for example,
Signal-to-Noise Ratios (SNRs), data rates, and so forth) or
capacities of radio channels between the transmit antennas and the
receive antennas using the pilot signals. They can then determine
effective channel information using measurements and feed back the
effective channel information to the transmitter. This effective
channel information is measured by the receivers. That is, each
receiver measures the channel qualities between the transmit
antennas and its receive antennas using different pilot signals
received from the transmit antennas of the transmitter and selects
an antenna offering the best channel quality in terms of
Signal-to-Interference Noise Ratio (SINR), capacity, throughput,
and data rate. The receiver then feeds back information about the
selected antenna to the transmitter.
Thus, the transmitter 100 receives effective channel information
from the receivers 200, 300 and 400 and calculates backward filter
information, forward filter information and scaling factors for the
receivers 200, 300 and 400. The backward filter information, the
forward filter information, and the scaling factors can be
calculated on a receiver-by-receiver basis. The transmitter
controls the power of transmission data and controls beamforming
using the backward filter information, the forward filter
information, and the scaling factors, for simultaneous data
transmission to the receiver 200, 300 and 400. Alternatively, the
transmitter 100 generates a channel matrix using the backward
filter information, the forward filter information and the scaling
factors and sends data simultaneously to the receivers 200, 300 and
400 based on the channel matrix. Also, the transmitter 100 signals
the scaling factors to the receivers 200, 300 and 400.
FIG. 2 is a flowchart illustrating a method for selecting the best
channel for a receiver in the multi-user MIMO system according to
an exemplary embodiment of the present invention.
Referring to FIG. 2, the transmitter sends pilot signals
periodically through the respective transmit antennas in steps
S100. Hence, a receiver with a plurality of antennas can receive
the pilot signals that may be different from one another.
Upon receipt of the pilot signals, the receiver measures the
qualities or capacities of a downlink channel in step S102. The
quality measurements include SINRs, data rates, or capacities. In
step S104, the receiver determines effective channel information
from the channel quality measurements. The effective channel
information is described as information indicating the channel
state of a receive antenna offering the best channel quality or
capacity among the receive antennas of the receiver. From the
perspective of the receiver, the effective channel information is
information about the best channel state in which data can be
received and can be expressed as a Hermitian matrix.
The receiver sends feedback information with the effective channel
information to the transmitter in step S106. The feedback
information contains channel information between the individual
antennas of the receiver and transmit antennas that offer good
channel qualities for the receive antennas, the channel qualities,
an effective channel quality value, and, if the antennas are
grouped, the indexes of the grouped antennas.
In step S108, the transmitter generates a channel matrix based on
effective channel information received from a plurality of
receivers. The channel matrix represents channel information
between the antennas of the transmitter and the antennas of the
receivers. The transmitter calculates filter information based on
the channel matrix in step S110. The filter information includes
backward filter information, forward filter information and scaling
factors for the receivers. The backward filter information is used
to control the power of transmission data and the forward filter
information is used for antenna beamforming or antenna grouping.
The scaling factors are the modulo levels of modulo operations and
sent to the receivers. The receivers use the inverses of the modulo
levels.
The transmitter generates an effective composite channel matrix or
parameter. The effective composite channel matrix or parameter is a
matrix with entries indicating the best channel qualities between
the transmit antennas and the receive antennas. The transmitter
provides a MIMO service simultaneously to the receivers using this
optimal matrix. In step S112, the transmitter sends the scaling
factors to the receivers.
FIG. 3 is a block diagram of a channel information extractor of the
receiver in the multi-user MIMO system according to an exemplary
embodiment of the present invention.
Referring to FIG. 3, the channel information extractor of the
receiver includes a receive beamformer 210 for measuring channel
qualities using pilot signals received from the transmit antennas
of the transmitter, a multiplier 220 for multiplying an input
signal by the inverse of a scaling factor received from the
transmitter, a modulo operator 230 for preventing a power increase
in the output signal of the multiplier 220, and a quantizer 240 for
quantizing the output signal of the modulo operator 230.
The multiplier 220, the modulo operator 230, and the quantizer 240
are allocated for each antenna. That is, these devices are provided
in a one-to-one correspondence to the antennas of the receiver.
The multiplier 220 multiplies an input signal by the inverse
1/.beta. of the received scaling factor .beta. representing the
modulo level of the transmitter.
As illustrated in FIG. 3, the receiver is provided with a plurality
of antennas, each receiving pilot signals from the transmitter. The
receive beamformer 210 measures the channel qualities of the pilot
signals received through each antennas.
The channel qualities, which can be expressed as an effective
Hermitian matrix, include SINRs and data rates. Then the receive
beamformer 210 determines effective channel information from the
channel quality measurements. The effective channel information is
calculated by
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times. ##EQU00003## diagonal matrix.
UU.sub.k.sup.H is known to the receiver. That is, the transmitter
periodically signals system parameters and transmitter-specific
information to all receivers. These receivers measure channel
qualities each time they receive the signal or when necessary for
system management. That is, the receiver performs a preliminary
operation on the signal received from the transmitter to determine
the effective channel information, for example, to calculate
H.sub.eff and n.sub.eff by Singular Value Decomposition (SVD).
After the receive beamforming, the received signal of all the
receivers is calculated by yy=H.sub.effx+n.sub.eff (6) where
H.sub.eff=[H.sub.eff,1.sup.T,H.sub.eff,2.sup.T, . . . ,
H.sub.eff,K.sup.T].sup.T, yy=[yy.sub.1.sup.T,yy.sub.2.sup.T, . . .
, yy.sub.K.sup.T].sup.T, and
n.sub.eff=[n.sub.eff,1.sup.T,n.sub.eff,2.sup.T, . . . ,
n.sub.eff,K.sup.T].sup.T.
When the receiver determines the effective channel information (for
example, H.sub.eff and n.sub.eff) in step S104 of FIG. 2, it sends
the feedback information with the effective channel information to
the transmitter in step S106.
FIG. 4 is a flowchart illustrating a channel information extracting
method of the receiver in the multi-user MIMO system according to
an exemplary embodiment of the present invention.
Referring to FIG. 4, upon receipt of pilot signals at each antenna
from the transmitter in step S200, the receiver measures channel
qualities using the pilot signals on an antenna basis in step S202.
The channel quality measurements include SINRs, data rates, and
Channel Quality Information (CQI). In step S204, the receiver
performs receive beamforming by multiplying a left unitary matrix
obtained by SVD. The SVD is an algorithm used to form a plurality
of spatial subchannels and achieve spatial multiplexing using a
plurality of transmit and receive antennas. The use of the SVD
enables separation of the spatial subchannels and provides spatial
multiple channels.
After steps S202 and S204, the receiver determines effective
channel information (H.sub.eff and n.sub.eff) by equation (5)
expressing the received signal after the receive beamforming in
step S206. In equation (5),
.times. ##EQU00004## corresponds to H.sub.eff and UU.sub.k.sup.H
corresponds to n.sub.eff. Equation (5) can be expressed as equation
(6). The receiver sends the effective channel information to the
transmitter in step S208. All receivers having connections in the
form of Hermitian matrices to the transmitter perform the same
algorithm of steps S200 to S208.
Upon receipt of a scaling factor from the transmitter in step S210,
the receiver multiplies received data or a received signal by the
scaling factor in step S212. The scaling factor is used to suppress
signal power.
FIG. 5 is a block diagram of a channel selector of a transmitter in
the multi-user MIMO system according to an exemplary embodiment of
the present invention.
Referring to FIG. 5, a transmitter 100 includes a THP part 110, a
beamforming part 120, and an extractor 130.
The extractor 130 receives feedback information including effective
channel information from a plurality of receivers and generates a
channel matrix using the received effective channel information.
Then, the extractor 130 calculates filter information channel by
channel or antenna by antenna in the channel matrix. The filter
information contains backward filter information B.sup.H, forward
filter information F.sup.H, and a scaling factor .beta.. The
extractor 130 generates a matrix using the filter information or
sends the filter information to a backward filter 116 of the THP
part 110 and a forward filter 122 of the beamforming part 120.
The THP part 110 includes a permutation matrix portion 112 having a
permutation matrix P representing the ordering of an input signal
vector u, the backward filter 116 for filtering the ordered signal
vector u by B.sup.H and a modulo operator 114 for reducing signal
power increased by B.sup.H. The backward filter 116 receives
B.sup.H for each channel from the extractor 130 and increases the
power of data by B.sup.H. The forward filter 122 receives F.sup.H
from the extractor 130 and sends data to one or more receivers by
antenna beamforming or antenna grouping using F.sup.H.
That is, the beamforming part 120 performs beamforming filtering on
the output signal v of the THP part 110 to obtain a transmission
signal vector x. The forward filter 122 acts a beamforming filter.
There are two constrains on precoding filters. One is to limit the
total transmit power and the other is imposed on the backward
filter information B.sup.H that must be strictly triangular. The
triangular structure ensures the causality of the feedback
process.
In operation, the extractor 130 receives effective channel
information (for example, H.sub.eff and n.sub.eff) for each antenna
from a plurality of receivers and generates a channel matrix based
on the effective channel information. The channel matrix represents
antennas offering good channel quality between the antennas of the
transmitter and those of the receivers. The extractor 130 then
calculates filter information for each receiver. The filter
information contains backward filter information B.sub.block.sup.H,
forward filter information F.sub.block.sup.H, and a scaling factor
.beta..sub.block.sup.H. Here, B.sub.block.sup.H=L.sub.block and
F.sub.block.sup.H=.beta..sub.block.sup.HH.sub.eff.sup.HP.sub.block.sup.TL-
.sub.block.sup.-HD.sub.block.sup.-1. .beta..sub.block.sup.H can be
calculated to satisfy transmit power. L.sub.block is a unit lower
triangular matrix and D.sub.block is a diagonal matrix, both being
calculated by
P.sub.block.PHI..sub.blockP.sub.block.sup.T=L.sub.blockD.sub.blockL.sub.b-
lock.sup.H (7) where
.PHI..sub.block=H.sub.effH.sub.eff.sup.H+.gamma..sup.-1I and
.gamma.=Es/trace(.phi..sub.n.sub.eff.sub.n.sub.eff)=Es/trace(.phi..sub.nn-
).
In this way, the extractor 130 calculates the filter information
and provides the backward filter information to the backward filter
116 and the forward filter information to the forward filter 122.
Thus, the transmitter can set up channels to carry data
simultaneously to the plurality of receivers or performing
beamforming for the transmit antennas.
The power of user data input to the permutation matrix portion 112
is increased by the backward filter and sent simultaneously to the
receivers on the channels by the forward filter.
FIG. 6 is a flowchart illustrating a channel selection method of
the transmitter in the multi-user MIMO system according to an
exemplary embodiment of the present invention.
Referring to FIG. 6, upon receipt of effective channel information
from a plurality of receivers in step S300, the transmitter
generates a channel matrix using the effective channel information
in step S302. The effective channel information of each receiver
represents information about a particular antenna that offers good
channel quality among the antennas of the receiver. The good
channel quality that the particular antenna offers from the
perspective of the receiver may not be good enough to the
transmitter. That is, even though the receiver wants to receive
data on the particular channel from the transmitter, the
transmitter may send the data on a different channel or may send no
data to the receiver. Hence, the channel matrix represents antennas
with good channel quality between the transmitter and the antennas
of the receivers. In step S304, the transmitter calculates filter
information using the channel matrix. The filter information
includes backward filter information, forward filter information
and a scaling factor. The backward filter information is a
reference value for controlling the signal power of data. That is,
the transmitter controls the power of transmission data using this
reference value. The forward filter information is a reference
value for antenna beamforming. That is, the transmitter determines
an antenna group or wirelessly connects a particular transmit
antenna to a particular receiver using the forward filter
information in order to provide a MIMO service.
The filter information calculation of step S304 is performed for
every receiver that has sent effective channel information. When
completing calculating the filter information for each receiver,
the transmitter applies the backward filter information to the
backward filter and the forward filter information to the forward
filter in step S308. In step S310, the transmitter amplifies the
power of input user data by the backward filter information and
performs antenna beamforming by the forward filter information. The
transmitter sends the user data input to the permutation matrix
portion 112 to the plurality of receivers in step S312.
In accordance with the present invention as described above, each
of a plurality of receivers can determine effective channel
information indicating an optimal antenna using pilot signals
received through a plurality of receive antennas. A transmitter can
receive the effective channel information from the receivers and
determines the best channels for the receivers within its service
area. Therefore, the amount of feedback information can be
decreased, thereby increasing system performance.
The above-described exemplary embodiments of an apparatus and
method for selecting channel in a multi-user MIMO system may be
recorded in computer-readable media including program instructions
to implement various operations embodied by a computer. The media
may also include, alone or in combination with the program
instructions, data files, data structures, and the like. The media
and program instructions may be those specially designed and
constructed for the purposes of the present invention, or they may
be of the kind well-known and available to those having skill in
the computer software arts. Examples of computer-readable media
include magnetic media such as hard disks, floppy disks, and
magnetic tape; optical media such as CD ROM disks and DVD;
magneto-optical media such as optical disks; and hardware devices
that are specially configured to store and perform program
instructions, such as read-only memory (ROM), random access memory
(RAM), flash memory, and the like. The media may also be a
transmission medium such as optical or metallic lines, wave guides,
and so on, including a carrier wave transmitting signals specifying
the program instructions, data structures, and so on. Examples of
program instructions include both machine code, such as produced by
a compiler, and files containing higher level code that may be
executed by the computer using an interpreter. The described
hardware devices may be configured to act as one or more software
modules in order to perform the operations of the above-described
embodiments of the present invention.
While the invention has been shown and described with reference to
the present invention thereof, it will be understood by those
skilled in the art that various changes in form and details may be
made therein without departing from the spirit and scope of the
present invention as defined by the appended claims and their
equivalents.
* * * * *